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Configuration principle of Transformer protection

 General configuration of transformer protection

  (1)buchholtz protecter 
  (2)differential protection
  (3)Over current protection or combined voltage blocking over current protection  
  (4)Zero sequence current protection
  (5)Zero sequence over-voltage protection
  (6)Over load protection 
   buchholtz protecter is the main protection of the internal fault of the transformer body.reflect various forms of the internal short circuit and  the reduced oil surface of the transformer.buchholtz protecter is divided into two types:the buchholtz protecter act instaneously when the internal had short circuit fault,each side of the transformer circuit breaker tripping,the oil surface of the transformer reduced e light and the internal has the buchholtz ,and the light  buchholtz  acted in the warning signal,it the transformer has equipped with the load voltage regulating device,there should be the heavy buchholtz and the light buchholtz.
  (2)  differential protection is the main protection of the internal ,bushing and the extraction line fault of the transformer. Which inflect the winding and outline of the interphase  short circuit of the transformer and the single phase ground short circuit of the neutral-point solid ground.whose action instantaneously break longitudinal differential protection for each side circuit breaker transformer,if the sensitivity of 110kV and 220kV of the single phase short circuit does not meet the requirements,there should add the zero sequence differential protection.Zero sequence differential protection only represents the Single phase earth fault,the requirements of action  in different with the Longitudinal differential protection.
  (3) Over current protection usually represents the over current protection of compound voltage lockout,Is the backup protection of the transformer.which reflects the transformer over current resulted by the external interphase short circuit.for the three winding transformer and self coupling transformer,installed in the side of the power supply and the main load side..if the sensitivity of the transformer does not meet the requirement,the over current protection device can be installed in both all the side.all the  directional element can be installed by the selective demand.
  (4) Zero sequence current protection is the backup protection of the transformer.which reflect the over current that resulted by the external single phase grounding fault of the three phase neutral grounding  system .The zero sequence current protection of the three winding transformer is connected to the neutral point current transformer.The zero sequence protection device of the self coupling transformer is installed on the zero sequence circuit of the high voltage side current transformer.when the two side have some grounding fault in the run or internal,if the sensitivity of the zero sequence protection,the zero sequence protection should be installed in the neutral point.
  (5)  for the transformer whose power in the low pressure side of the zero sequence over voltage.if the neutral point maybe run in the ground or not in the ground,not only the zero sequence but also the zero sequence voltage protection should be installed in the over voltage that caused by the external single grounding and the over voltage that caused by the lost neutral point .the protection action will break after one time delay.
  (6) the over load protection of the over load protection transformer can reflect the condition of the common winding and each side over load.all the over load protection act by the monomial and time limit.  
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